Modelling stress relaxation for viscoelastic material with many time steps

- January 26, 2024 at 11:18 am
  
  Thies Blaakman
  Subscriber
  
  Dear all,
  I'm trying to model the stress relaxation behaviour of a material after deforming it. I have curve fitted the Prony series for this model to make my material behave viscoelastically and I have some generic linear elastic properties. In order to deform the model, I need many time steps in order to have a converging solution, but these timesteps already include some stress relaxation behaviour due to the viscoelastic material model. I would like to create a seemingly instantaneous linear elastic deformation, then activate the viscoelastic properties and see what happens. I have tried using the MPCHG command, but this of course does not work for nonlinear material models. Is there anyone who can give me a lead on this?
  With kind regards,
  Thies
- January 29, 2024 at 4:35 pm
  
  Giorgos Papa
  Ansys Employee
  
  Hello Thies,
  
  Unfortunately it is not possible to turn off/on the viscoelasticity like we allow for creep.
  One thing you can do is run the first load step with a very small time to make the rate dependency negligible.
  
  Kind Regards,
  Giorgos
  - January 30, 2024 at 8:44 am
    
    Thies Blaakman
    Subscriber
    
    Dear Giorgos,
    That's kind of the problem. If I don't use many time steps to subdivide my deflection, I won't have convergence. Is there maybe a way to solve my model elastically, and then load it in a different file with a different material model in which I add the viscoelasticity?
    With kind regards,
    Thies